Internal combustion engine with direct gasoline injection and controlled ignition

ABSTRACT

The invention relates to an internal combustion engine with direct gasoline injection and controlled ignition, comprising at least one cylinder ( 1 ), a cylinder head ( 6 ), sealing the cylinder ( 1 ), a piston ( 7 ), arranged to run in the cylinder ( 1 ), a combustion chamber ( 2 ), defined by the piston ( 7 ) and the cylinder head ( 6 ), a gasoline injection means ( 3 ) into the combustion chamber ( 2 ), an ignition means ( 4 ), for producing an ignition of the air/gasoline mixture in the combustion chamber ( 2 ), inlet ( 8 ) and exhaust ( 9 ) valves, selectively sealing the combustion chamber ( 2 ) and means for recirculation of at least a part of the exhaust gas into the combustion chamber ( 2 ) during the air intake phase, characterized in that wherein the pressure provided for the injection means ( 3 ) is greater than 250 bars, such as to homogenize the air/gasoline/recycled exhaust gas mixture and increase the speed of combustion.

The invention concerns an internal combustion engine with directgasoline injection and controlled ignition.

The invention concerns more particularly an internal combustion engine,with direct gasoline injection and controlled ignition, comprising atleast one cylinder, a cylinder head closing the cylinder, a pistonsliding in the cylinder, a combustion chamber defined between the pistonand the cylinder head, means for injecting gasoline into the combustionchamber, ignition means intended to produce an ignition of theair-gasoline mixture in the combustion chamber, intake and exhaustvalves, selectively closing the combustion chamber, and means forrecirculating at least a portion of the exhaust gases into thecombustion chamber during the air intake phase.

Various modes of operation in connection to the injection strategy canbe envisioned thanks to the direct injection of gasoline.

One of the known solutions is the introduction of fuel in stoichiometricproportions, so that the totality of the fuel is burned upon contactwith the air. According to this solution, the fuel is introduced earlyenough during the intake phase of the engine cycle to ensure a goodevaporation and a good homogeneity of the load.

In this mode of operation, it is interesting to introduce into thecombustion chamber, at the time of intake, burned gases from the exhaust(also called recirculated gases). These gases do not participate in thecombustion but they make it possible to reduce the density of the fuelmixture (gasoline-air) and thus to reduce the loss of energy during theengine cycle.

However, the reintroduction of burned gases has drawbacks: theair-gasoline-recirculated gases mixture is not homogeneous and thecombustion speed is reduced. These two effects result in a degradationof the combustion efficiency. The maximum amount of burned gases that itis possible to reintroduce to improve consumption is thus limited.

An objective of the present invention is to remedy all or part of thedrawbacks of the prior art mentioned above.

To this effect, the internal combustion engine, with direct gasolineinjection and controlled injection according to the invention, which isotherwise conform to the generic definition given in the preamble above,is essentially characterized in that the pressure provided to theinjection means is above 250 bars, so as to homogenize theair-gasoline-recirculated gases mixture and to increase the combustionspeed.

Further, the invention can comprise one or several of the followingcharacteristics:

The exhaust gases reintroduced into the combustion chamber represent aresidual ratio above 20%, and preferably comprised between 40 and 60%,

at least a portion of the recirculated exhaust gases is reintroducedinto the combustion chamber by a so-called “external” route (EGR), i.e.,via a derivation conduit,

at least a portion of the recirculated gases is reintroduced into thecombustion chamber by a so-called “internal” route (IGR), i.e., byappropriate control of the intake and exhaust valves.

the gasoline injection means and the ignition means are separated by adistance comprised between 5 and 30 millimeters.

the injection means and the ignition means are disposed in the cylinderhead according to two respective axes forming an angle above 35°.

the injection means inject gasoline during the intake phase of theengine cycle.

Other particularities and advantages will appear upon reading thefollowing description made in reference to the drawings in which:

FIG. 1 is a schematic and partial cross-section view of an internalcombustion engine according to the invention,

FIG. 2 is a schematic top view of an engine comprising a known exhaustgas recycling device by a so-called “external” route.

The engine according to the invention shown on FIG. 1 comprises at leastone cylinder 1, a cylinder head 6 closing the cylinder 1, and a piston 7slidingly arranged in the cylinder 1. A combustion chamber 2 is definedbetween the piston 7 and the cylinder head 6.

The engine comprises also a gasoline injection means 3, such as a nozzleor an injector which opens into the combustion chamber 2. The injector 3is supplied by an injection pump 13 intended to provide pressurizedgasoline to injector 3. Ignition means 4, such as a spark plug, plungealso into the combustion chamber 2 for producing an ignition of theair-gasoline mixture in the combustion chamber 2 at a determined time.

According to a characteristics of the invention, the pressure of thegasoline provided to the injector 3 is above 250 bars. The injector 3can be disposed, for example, on the symmetry axis Z of the cylinder 1,such as shown on FIG. 1. The spark plug can be disposed at a distancecomprised between 5 and 30 millimeters of the injector 3. According tothis arrangement, the injector 3 is diposed, in the cylinder head 6,along an axis X, and the spark plug 4 is disposed along an axis Y. Theangle θ between the axis X of the injector 3 and the axis Y of the sparkplug 4 is under 35°.

Other arrangements, not shown, of the injector 3 and the spark plug 4can be envisioned. For example, the angle θ between the axis X of theinjector 3 and the axis Y of the spark plug 4 is above 35°, and,preferably, equal to about 60°. The injector 3 and the spark plug 4 canbe disposed in particular on opposite sides of the symmetry axis Z ofthe cylinder 1.

The engine comprises also one or several intake valves 8 and one orseveral exhaust valves 9 selectively closing passages between thecombustion chamber 2 and, respectively, an intake conduit 10 and anexhaust conduit 11.

In addition, the engine is characterized in that it comprises means forrecirculating at least a portion of the exhaust gases.

During injection of the high pressure gasoline according to theinvention, strong turbulences are observed in the combustion chamber 2,far above those of conventional arrangements. This turbulence makes itpossible to increase the folding of the flame front and thus the flamesurface in contact with the fuel mixture.

The strong turbulence, generated by the high gasoline pressure, allowshigher combustion speeds for a given ratio of burned gases. Thus, itwill be possible to obtain a combustion of acceptable quality with highratios of recirculated gases. It will be possible to have a residualratio of exhaust gases reintroduced into the combustion chamber 2 above20% and, according to a preferred embodiment, comprised between 40 and60%.

Further, the high pressure delivered makes it possible to inject a largeamount of fuel thanks to the good atomization obtained. Thischaracteristics makes it possible also to obtain a very homogeneousfresh air-burned gases-air mixture quickly.

The engine according to the invention has the advantage that it reducesfuel consumption thanks to the more important recirculation of exhaustgases.

Two known means for recirculating burned gases can be envisioned: eitherby the so-called “external” route (EGR), as shown on FIG. 2, or by theso-called “internal” route (IGR).

According to the configuration by the so-called “external” route, theburned gases can be taken according to two modes.

As a variant, the burned gases can be taken in the area of the exhaustconduits 11. The gases are reintroduced subsequently upstream from theintake collector 16 via a derivation conduit 14.

The burned gases can be taken via an internal conduit 15 in the area ofthe cylinder head 6. The gases are subsequently reintroduced upstream ofthe intake collector 16.

In both cases, the amount of reintroduced exhaust gases is controlled bya regulation valve 12 controlled by an engine calculator (ECU), notshown. The burned gases mix with the fresh air. This mixture isintroduced into the combustion chamber during the intake phase.

According to the configuration by the so-called “internal” route, theburned gases can be introduced by appropriate control of the intakevalves 8 and exhaust valves 9. In a known manner, when a combustioncycle is completed, the exhaust valves 9 open so as to release theburned gases. In order to recuperate a portion of the burned gases, theintake valves 8 open during the gas exhaust phase. At that time, thepressure in the exhaust conduit 11 is substantially higher than thepressure observed in the intake conduit 10.

This pressure difference triggers an aspiration of the burned gases intothe intake conduit 10 during the phase corresponding to the commonopening of the intake valves 8 and exhaust valves 9. The opening of theintake valve 8 continues after the closing of the exhaust valve 9.During this period, the burned gases sucked into the intake conduit 10are reintroduced into the combustion chamber 2.

The control of the amount of reintroduced burned gases is obtained bycontrolling the opening of the intake valve 8. The use of camshaftphase-shifting systems makes it possible, for example, to capture intothe engine large amounts of burned gases (up to 80% by weight).

Preferably, the gasoline injection is made, in a preferential manner,during a very short period, as close as possible to the ignitioninstant. In particular, it will be possible to have the gasolineinjection take place during the compression phase of the engine cycle.Thus, the strong turbulence generated by the gasoline jet will bemaintained and amplified during the beginning of combustion. The use ofan injection pressure above 250 bars ensures a good homogeneity of themixture in spite of the late time of injection.

The performance of the engine, at full load, will be improved also byadapting the shape of the intake conduits 10. Since it is no longerrequired that the aerodynamics be generated by the intake conduits, itwill be possible to optimize their shape to ensure a better filling ofthe engine under heavy load.

1. Internal combustion engine, with direct gasoline injection andcontrolled injection, comprising at least one cylinder, a cylinder headclosing the cylinder, a piston slidingly arranged in the cylinder, acombustion chamber defined between the piston and the cylinder head,means for injecting gasoline into the combustion chamber, ignition meansintended to produce an ignition of the air-gasoline mixture in thecombustion chamber, intake valves and exhaust valves, selectivelyclosing the combustion chamber and means for recirculating at least aportion of the exhaust gases into the combustion chamber during the airintake phase, wherein the pressure provided to the injection means isabove 250 bars, so as to homogenize the air-gasoline-recirculatedexhaust gases mixture and to increase the combustion speed.
 2. Engineaccording to claim 1, wherein the exhaust gases reintroduced into thecombustion chamber represent a residual ratio above 20%.
 3. Engineaccording to claim 1, wherein at least a portion of the recirculatedexhaust gases is reintroduced into the combustion chamber by a so-called“external” route (EGR), i.e., via a derivation conduit.
 4. Engineaccording to claim 1, wherein at least a portion of the recirculatedexhaust gases is reintroduced into the combustion chamber via aso-called “internal” route (IGR), i.e., by appropriate control of theintake valves and exhaust valves.
 5. Engine according to claim 1,wherein the gasoline injection means and the ignition means areseparated by a distance comprised between 5 and 30 millimeters. 6.Engine according to claim 1, wherein the injection means and theignition means are disposed in the cylinder head according to tworespective axes forming an angle (θ) above 35°.
 7. Engine according toclaim 1, wherein the injection means inject gasoline during thecompression phase of the engine cycle.
 8. Engine according to claim 1,wherein the injection means inject gasoline during the intake phase ofthe engine cycle.
 9. Engine according to claim 2, wherein the exhaustgases reintroduced into the combustion chamber represent a residualratio comprised between 40 and 60%.